Added a seekTo function and fixed a nasty reconnect issue

- I needed a seekTo function and felt it was kind of silly having to calculate a relative seek, so I added it as a function and made the relative seek call seekTo.
- Now uses callback in connect if it is present.
- ~~Added self as an instance variable in init, this saves us having to set self in all other function calls.~~
  - Reverted this due to possible issues on re-use of device in different contexts.
- Fixed an issue when re-using a device and calling connect after having called stop.
- Updated to castv2-client version 0.0.8, brings some nice fixes and better volume handling.
- Fixed setVolume not working, due to changes in castv2-client
  - setVolume was changed in castv2-client v0.0.8: https://github.com/thibauts/node-castv2-client/commit/c01c7c40b01c02c8cfdff7bcb6443ef42ecb42de
- Added setVolumeMuted call since this was now made possible by above castv2-client change
  - This is nice to have since muting remembers where the volume was last at when unmuting.
- Added close call to end the underlying castv2 connection.
- Added test for re-use and re-connection of device.
- Fixed and added untested calls to original test.